The fakir, the Muslim Holy Man, in The Monkey's Paw,wanted 'to show that fate ruled people's lives, and that those who interfered with it did so to their sorrow.' Both the White Family and Macbeth 'interfered' with Fate by employing supernatural means to try to shape their own futures. They both suffer terrible consequences.
So firstly, it is not for ordinary human beings to tamper with fate/ the future. But on the other hand,both the witches and the monkey's paw have extra-ordinary, supernatural powers. The witches for example, can see inside Macbeth's head and know that he has ambitions to become king. THe monkey's paw, as in a fairy tale, is able to make wishes come true; furthermore, it is seemingly able to bring Herbert White back from the dead.
But to mess with Fate is seen as evil and both the witches and the monkey's paw are evil: the witches' predictions are tricks which reassure Macbeth but come true in unexpected, terrifying ways: so when the witches say 'none of woman born / Shall harm Macbeth' it does not mean, as he believes, he is invincible; it means he will be killed by Macduff who was born by Caesarean section.
The Whites' wishes come true but also in unexpected, terrifying ways: they get the money they wished for, but it is compensation for the fatal works injury to Herbert they never would have desired.
In both stories there is a warning against tempting fate.The Whites are warned against using the paw by the sergeant-major and Macbeth is warned against heeding the witches by Banquo. When they don't heed these warnings, we see that tempting Fate plunges you into Hell; in The Monkey's Paw there is the nightmarish vision of old man White struggling with his wife to lock the door against 'the thing outside', the horrific zombie that their son has become. Macbeth is plagued by hellish visions throughout, like the floating dagger and worse the ghost of the murdered Banquo.
The message is clear: mere mortals like Macbeth or the Whites, attempt to interfere with Fate/ the future at their peril. They both should have been happy with what Fate decided they should have: the Whites with their loving though not rich family; Macbeth with the position of Thane of Cawdor which he earned, unlike the Kingship which he seized by force and murder.
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